HO, or hydroxyl, is a functional group consisting of an oxygen atom bonded to a hydrogen atom. It is commonly found in various organic compounds, including alcohols and phenols. The presence of the hydroxyl group can significantly influence the chemical properties of a molecule, such as its solubility and reactivity. In chemistry, hydroxyl groups are important for forming hydrogen bonds, which can affect the boiling and melting points of substances. For example, in water, the hydroxyl group contributes to its unique properties, making it essential for life. Hydroxyl groups also play a crucial role in biochemical processes, such as those involving enzymes and metabolism.